1) Field of the Invention
The invention relates to a multi-stage steam-power/working process for the generation of electric energy in a cycle by the use of an additional gaseous energy carrier for increasing the pressure, temperature and mass of the working fluid in the power process and for the recirculation of the working fluid in the working process.
Such a technical solution is primarily required in the area of power economy.
2) Discussion of the Relate Art
During the conversion of thermal energy into mechanical energy, the efficiency is limited to maximum values which are determined by the temperatures of the combustion, of the exhaust gas released during the combustion and of the coolants used. Material limits in the energy-conversion processes applied influence the difference between the theoretically attainable efficiency and the practically realized efficiency according to the respective prior art. Since turbomachine research has already reached a very high level of development, possible marked improvements result essentially from the thermodynamics of the cycles.
Starting from the maximum combustion temperatures, the general temperatures in the energy-conversion process, according to the previous level of knowledge, have to be increased in order to increase the exergy portion.
In addition, when fossil fuels are used in the gas-turbine process, the high combustion temperatures have an effect on the emission of nitric oxide.
For the generation of electric energy, the steam-turbine Rankine cycle, the gas-turbine cycle and the gas-and-steam combined process (CCPP process) as the combination of both basic processes have proved successful on a large scale.
By means of modern steam-power processes, the intended improvements in efficiency are to be achieved by pressure and temperature increases of the working fluid to over 300 bar and over 700xc2x0 C. At the same time, this requires solutions in terms of materials for coping with these process parameters.
By means of modern gas-turbine processes, the aim is to increase the turbine application temperatures to over 1500xc2x0 C. and to obtain the stability of the material used by adequate technical solutions for machine cooling.
In known gas-and-steam combined processes (CCPP), benefits are obtained from technical developments in the fields of both basic processes.
In the effort to achieve the improvements in efficiency aimed at in the conversion of energy, attempts have been made to find solutions for the most favorable configuration of the energy-conversion processes by utilizing cycles.
Thus, U.S. Pat. No. 3,841,100 describes a closed gas-turbine process, using various gases, such as air, hydrogen, helium or other gases, in which the working process takes place in a turbocompressor and the power process takes place in a gas turbine. In this case, the intended improvement in efficiency is to be achieved through the use of an extremely large coolant reservoir, by means of which the improved cooling capacity of ambient air during the nighttime can be utilized. At the same time, the continuous operation of the plant at rated load is to be ensured. This illustrates the great technical efforts which are made in order to obtain relatively small improvements in efficiency.
The object of the invention is therefore to develop the closed cycle for generating electric energy in such a way that the shortcomings of the known prior art are overcome and at the same time improvements in efficiency can be achieved. The general temperature and pressure requirements of the working fluid used are to be markedly reducible compared with known techniques.
At the same time, despite fluctuating load requirements, the aim is to provide the technical solution to be developed with the prerequisites for continuous operation under rated load.
According to the invention, a multi-stage steam-power and steam working process for the generation of electric energy in a cycle by the use of an additional gaseous energy carrier for increasing the pressure, temperature and mass of the working fluid in the cycle and for the recirculation of the working fluid in the cycle is configured in such a way that continuously superheated steam is used as a working fluid.
With this selection of the working fluid, the favorable properties of the steam with regard to the specific heat, with regard to the specific pressure losses and with regard to the coefficient of heat transfer can be utilized.
The power process is carried out in a closed multi-stage gas-turbine plant, the steam used, in the superheated form applied, exhibiting an increasingly gas-like behavior.
The working fluid is stored as condensate before start-up and after shutdown in a working-fluid storage vessel arranged between the prime mover and the driven machine. To this end, this working-fluid storage vessel equipped with technical means for evaporating the condensate or for cooling the steam as and when required.
Furthermore, the proposed technical solution is characterized in that the conversion of the stored energy of the working fluid and of the additionally used gaseous energy carrier into mechanical energy is carried out by means of a closed gas-turbine plant. The cycle is maintained by the use of hydrogen and oxygen as additional gaseous energy carrier and the resulting steam from the oxyhydrogen gas reaction taking place in the gas turbine.
The additional vaporous working fluid resulting from the internal combustion of the hydrogen and oxygen used is used as superheated steam for the purpose of increasing the pressure, temperature and mass of the entire working fluid directly at the blading of the multi-stage gas turbine. Due to the shifting of the oxyhydrogen gas reaction into the individual stages of the multi-stage gas turbine, the high pressures and temperatures resulting in the process, with minimum transfer losses, are utilized for the power process without the general pressure and temperature levels in the entire cycle having to be maintained.
After the expansion in the gas turbine, the superheated steam used is fed as working fluid together with the superheated steam as the conversion product from the controlled oxyhydrogen gas reaction to the compression stage of the cycle.
It is essential to the invention that the thermal energy of the expanded gas-turbine exhaust steam is used by means of heat exchanger for pre-superheating the compressed superheated steam as working fluid. In this case, the desirable cooling of the working fluid is effected at the same time before it is used in the intended turbocompressor.
Substantial portions of the cooling tasks in the cycle are therefore covered by the heat exchange between the expanded working fluid of high temperature and the compressed working fluid of low temperature.
In one embodiment of the invention, the working fluid between the prime mover and the driven machine is evaporated in a working-fluid storage vessel by the external supply of energy before start-up of the plant. In this case, the working fluid in the working-fluid storage vessel is in the form of steam condensate.
In another embodiment, provision is made for the excess working fluid, which approximately corresponds to the quantity of the steam produced from the combustion reaction of hydrogen and oxygen, to be extracted from the cycle between the prime mover and the driven machine.
In principle, the entire cycle is thus suitable for the discharge of excess working fluid, in which case, in accordance with the actual requirements for the efficient utilization of the extracted working fluid, for example for heating purposes, the compressed steam used for the turbine cooling may also be removed from the cycle.
It is also possible to use excess portions of the electric energy generated in the cycle for producing hydrogen and oxygen. This is especially suitable if, despite reduced load requirements, the cycle is maintained under rated load in the interest of utilizing the highest possible efficiencies.
Provision is likewise made for tapped portions of the working fluid in the form of steam from the compression stage of the cycle to be used for the purpose of cooling the shaft and the blades of the gas turbine.
In summary, the advantages of the proposed solution in terms of the method consist in the fact that, while avoiding air pollutants from the cycle, continuous operation can be carried out with superheated steam as working fluid without having to forego the known technical advantages of the gas-and-steam combined process. In addition, the advantage consists in the fact that the general pressure and temperature levels in the closed cycle are markedly reduced compared with comparable technical plants. This permits more cost-effective machine solutions, which in addition may have increased fatigue strength. In addition, the advantageous physical properties of superheated steam are crucial prerequisites for comparatively small specific dimensions of the plant components, such as driven machine and prime mover, connecting pipelines or heat-exchanger areas.
The proposed arrangement for carrying out the multi-stage steam-power and steam-working process according to the method described consists of a multi-stage gas turbine as prime mover and a multi-stage turbocompressor, arranged on the turbine shaft, as driven machine, and of the connecting pipelines for the circulation of the working fluid.
In this case, feed devices for gaseous hydrogen and gaseous oxygen are arranged at the individual turbine stages in the direct vicinity of the blading.
A heat exchanger serving to transfer heat from the expanded turbine exhaust steam to the compressed working fluid is arranged between the driven machine and the prime mover.
In addition, a working-fluid storage vessel is arranged between the driven machine and the prime mover. Such heat-exchanger areas serving to cool the compressed working fluid are likewise arranged in the individual stages of the turbocompressor plant.
In a special embodiment of the arrangement for carrying out the multi-stage steam-power and steam-working process, an evaporation plant serving for the plant start-up and intended for the working fluid is arranged in the working-fluid storage vessel.
A further embodiment of the arrangement for carrying out the multi-stage steam-power and steam-working process provides for a working-fluid extraction device serving to regulate a constant mass flow for the compression unit to be arranged between prime mover and driven machine.
An energy-conversion plant provided with said features is characterized by a number of advantages. Due to the exclusive use of superheated steam as working fluid, the known physical advantages of this working fluid can be utilized for the simple and cost-effective configuration of the requisite plant components for performing the cycle.
The direct arrangement of the feed devices for gaseous hydrogen and gaseous oxygen at the blading of the individual stages of the gas turbine enable undesirable load peaks to be largely eliminated and the requisite high pressure and temperature resistance of the plant components used to be restricted to the corresponding turbine stages.
In addition, the uniform use of superheated steam as working fluid for the cycle enables the advantageous characteristics of the working fluid to be utilized for the arrangement of heat-exchanger areas of comparatively small dimensions.
It may also be regarded as an advantage that the components serving to cool the units, to store the working fluid and to remove the working fluid are to be designed solely for the use of superheated steam or steam condensate.
The proposed solution on the whole thus offers the prerequisite for providing compact energy-conversion plants of high energetic efficiency at a comparatively low specific machine cost.